1. Field of the Invention
The invention relates to a light source system, more particularly to a light-emitting diode light source system.
2. Description of the Related Art
As shown in FIG. 1 and FIG. 2, an optical engine in a conventional projector normally uses a gas discharge lamp 11 as its light source for optical projection. There are two kinds of reflectors for the gas discharge lamp 11, i.e., a parabolic reflector 12 (as shown in FIG. 1) and an elliptical reflector 12′ (as shown in FIG. 2). The reflector 12, 12′ directs light beams generated by the gas discharge lamp 11 toward an optical system. The optical system can include an array of lenses 13 (as shown in FIG. 1), or can include an assembly of a color wheel 18 and an integration rod 14 (as shown in FIG. 2). The optical system filters, homogenizes and focuses the source light provided by the gas discharge lamp 11 toward a light valve 15. Eventually, the light valve 15 converts the light beams into an image light output, which is then projected onto a screen (not shown) via a projection lens (not shown). However, the gas discharge lamp 11 is not only expensive and has a short service life (approximately 3,000 to 10,000 hours), but the gas discharge lamp 11 also emits ultraviolet light when generating the source light, such that it is required that the gas discharge lamp 11 be isolated from other components to avoid damage due to the ultraviolet light. In addition, the gas discharge lamp 11 does not comply with the environmental friendly “green product” standard because it contains mercury.
Since the light-emitting diode (LED) has a long service life, which can reach up to 100,000 hours, is environmental friendly (does not contain mercury), and has a good color rendering property, etc., light sources utilizing LEDs are also available. As shown in FIG. 3, a plurality of LEDs 16 are packaged onto a substrate 17, and are used with an integration rod 19 and a lens unit 10 of an optical system. Light beams provided by the LEDs 16 enter a light incident side of the integration rod 19 to be homogenized by the integration rod 19. The light beams emerge out of a light exit side of the integration rod 19, pass through the lens unit 10, and propagate toward a light valve 15. However, the light incident side of the integration rod 19 is often relatively small, such that only a portion of the light beams provided by approximately three or four LEDs 16 is able to enter the integration rod 19 through the light incident side. Therefore, the luminance of the whole optical system is limited by the capacity of the integration rod 19. In other words, even if the total number of LEDs 16 is increased, usable light is still limited due to the limited luminous flux of the optical system. As a result, increasing the number of LEDs 16 would not increase the luminance of the system, but is also a waste of energy and cost. In addition, since the LEDs 16 need to be concentrated near the light incident side of the integration rod 19 in order to allow a maximum amount of light beams to enter the integration rod 19, dissipation of heat energy generated by the LEDs 16 is difficult, thereby adversely affecting illuminating efficiency of the LEDs 16. Therefore, how to improve the optical utilization efficiency of the LEDs 16, and how to increase the luminance of the optical system are major issues in the relevant field.